This proposal describes the use of structural biology design principles to define key interventional epitopes for vaccine development. This effort is piloted by targeting the pic gene of Shigella flexneri, important in pathogenesis of dysentery. The long-range goal is to develop a panel of structural epitopes, within a large family of pathogenic molecules, which can provide a safe and broad vaccine component for many diarrheal and mucosal diseases. A newly discovered family of enteric disease associated proteins share a common secretory pathway. These proteins are classified as "autotransporters", based on their ability to self-direct membrane translocation and cleavage to produce a secreted mature protein. This is accomplished through structural motifs inherent in the precursor molecule that spontaneously form a membrane pore through which the mature domain of the molecule is translocated. Members of this family include the Shigella pic gene, the Neisseria secretory IgA protease, and the Helicobacter vacA toxin, with many other examples of toxins or biochemical properties linked to colonization or cell invasion. The identification of common structural motifs utilized by this family of proteins will test development of a broad based vaccine strategy designed to block secretion of the disease-associated activities. Principles of computational homology modeling, in combination with phylogenetic comparisons, have predicted surface exposed structural epitopes for vaccine responses. Preliminary data identifying such structural epitopes now allows immunogenicity testing and proof-of-principle studies to demonstrate that vaccine strategies can effectively block secretion and function within this class of proteins.